1. Field of the Invention
This invention relates in general to the manufacture of magnetic heads, and more particularly to a lapping method and station to achieve tight dimension controls for both read and write elements of magnetic recording heads and magnetic storage device formed thereby.
2. Description of Related Art
Fixed magnetic storage systems are now commonplace as a main non-volatile storage in modem personal computers, workstations, and portable computers. Storage systems are now capable of storing hundreds of gigabytes of digital data, even when implemented in portable computers.
As disk drive technology progresses, more data is compressed into smaller areas. Increasing data density is dependent upon read/write heads fabricated with smaller geometries capable of magnetizing or sensing the magnetization of correspondingly smaller areas on the magnetic disk. The advance in magnetic head technology has led to heads fabricated using processes similar to those used in the manufacture of semiconductor devices.
A typical disk drive is comprised of a magnetic recording medium in the form of a disk for storing information, and a magnetic recording head for reading or writing information on the disk. The disk rotates on a spindle controlled by a drive motor and the magnetic recording head is attached to a slider supported above the disk by an actuator arm. When the disk rotates at high speed a cushion of moving air is formed lifting the air bearing surface (ABS) of the magnetic recording head above the surface of the disk.
The write portion of a recording head is typically fabricated using a coil embedded in an insulator between a top and bottom magnetic layer. The magnetic layers are arranged as a magnetic circuit, with pole tips forming a magnetic gap at the air bearing surface of the head. When a data bit is to be written to the disk, the disk drive circuitry sends current through the coil creating a magnetic flux. The magnetic layers provide a path for the flux and a magnetic field generated at the pole tips magnetizes a small portion of the magnetic disk, thereby storing a data bit on the disk.
The read portion of the magnetic recording head is typically formed using a magnetoresistive (MR) element. This element is a layered structure with one or more layers of material exhibiting the magnetoresistive effect. The resistance of a magnetoresistive element changes when the element is in the presence of a magnetic field. Data bits are stored on the disk as small, magnetized region on the disk. As the disk passes by beneath the surface of the magnetoresistive material in the read head, the resistance of the material changes and this change is sensed by the disk drive control circuitry.
Multiple magnetic recording heads are built in a wafer via lithographic and film deposition process. The wafer is processed to form multiple pieces (each piece is called a slider); on each piece there is one magnetic recording head. The sliders are then polished to achieve both flat surface, on which ABS is formed, and the desired stripe height for the reading head and throat heights for writing head.
The targeted dimension for a reader, stripe height (SH) is determined according to, for example, an Electronic Lapping Guide (ELG) or its direct resistance value. The height of write element (throat height) is neither monitored nor actively controlled. The final throat height is determined by the final stripe height and the offset between the read and write element, which is defined in the wafer fabrication process. Variations of final throat height result from wafer and slider fabrication processes. Wafer processes cause variations of final throat height because read and write elements are physically separated in two layers (between 8-10 microns), and these generally cannot be aligned to better than 30 nm. Slider fabrication processes also cause variations in final throat height because due to the physical separation of the read and write elements, any wedge angle during lapping will translate to different removal of read and write elements. For example a 5 um (Δ) wedge over a slider body length of L=1.25 mm will cause 40 nm (δ) difference in removal between a read and write elements separated 10 um apart (d). Currently, the wedge is neither monitored nor controlled.
For longitudinal recording heads, the throat height control is not currently as critical to the write element performance and the tolerance of both wafer and slider fabrication process is acceptable. But as the longitudinal recording heads can no longer support the aerial density growth of magnetic recording technology, perpendicular recording heads are the necessary technology for the future. For perpendicular recording heads, the throat height control is as important as the stripe height control.
It can be seen that there is a need to control stripe height and throat height of magnetic recording heads with a higher precision (e.g., better than 10 nm) than is available from current lithographic and lapping processes.